I don't think "fedup" was introduced until F18 or so.
The new version of this software program usually attend to replace the old software because this new software include patch and fix bug, fix security vulnerabilities, add new futures and sometimes they improve capabilities and performance of the software itself.There is lot of software tools and software interface available, that can be use to update Fedora...Popping a new F21 or F22 (next week) disk/ USB into the drive would be the best way to go.However if you really must or just want a challenge, then here are the 'official' upgrade paths; Upgrading from EOL Fedora using yum, and if you should fail at said challange then you can either; a, revert to the backup you took and try again or b, give in and install F21/22 from scratch and restoring all your files from the backups you took.Its unlikely Fedup is going to be able to jump you from F14 to F21.
I would suggest you back-up any data you want to save, create a LIve CD, and use the install to hardware feature of the CD to build a new system. F14 is long gone now so "update" is not going to find the repository.
The answer on why we need to update fedora regularly is because that, the software that comes on Fedora installation CD or DVD usually out of date by the time you installing them...
and new version of software program usually available for you to download and ready to replace the old version of software program inside your system.
These are live cds which you can run and then decide to install or not.
Or you can install the f21 released dvds which are Workstation or Server, or you could download the netinstall cd and do a netinstall which will set up a current upgraded system by downloading.
and you may notice that yum command ask your permission to install update for your system...